Torpedo drag reduction apparatus



May 14, 1968 w. F. MADISON TORPEDO DRAG REDUCTION APPARATUS 2 Sheets-Sheet 1 Filed Aug. 31, 1967 INVENTOR. WILLIAM F. MADISON MICHAEL F. OGLO ROY MILLER ATTORNEYS.

y 1968 w. P. MADISON 3,382,831

TORPEDO DRAG REDUCTION APPARATUS Filed Aug. 31, 1967 2 Sheets-Sheet 2 FIG. 4.

United States Patent 3,382,831 TORPEDO DRAG REDUCTION APPARATUS William F. Madison, Arcadia, Calif., assignor to the United States of America as represented by the Secretary of the Navy Filed Aug. 31, 1967, Ser. No. 665,675

. 3 Claims. (Cl. 114-20) ABSTRACT OF THE DISCLOSURE An annular chamber is formed between the nose fair ing wall and an inner pressure hull of a torpedo. Ambient seawater, under ram pressure, is ingested by scoops and introduced into the rear end of the chamber. Contained in the longitudinal expanse of the chamber is an annular, radially foraminous, ablative cake of polymer material of the hydrodynamic drag reducing type. The radial thickness of the ablative cake is smaller than that of the annular chamber to allow annular space between the outside surface of the polymer cake and the interior of the fairing wall, and annular space between the inside surface of the annular cake and the outside of the pressure hull. A labyrinth bailie structure is placed in these annular spaces to alternately direct the seawater radially inwardly, and radially outwardly, through successive axial sections of the radially foraminous cake. The front end of the annular chamber is communicated with the exterior of the surface of the torpedo hull by a circumferential slot which extends continuously about the torpedo. The solution of seawater and polymer resulting from the circulation of the water through the labyrinth issues forth through the slot into the boundary layer flow under the ram pressure.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to improved torpedo apparatus of the type employing the introduction of an aqueous solution of certain polymer additives into the boundary layer flow about the torpedo. The polymer additives referred to are characterized as being water soluble and having a high molecular weight and a long-chain molecular structure. Included among effective drag-reducing polymers are poly- (ethylene oxide), and polyacrylamide.

It can be theoretically demonstrated that carrying a polymer additive within the torpedo, and continuously mixing and ejecting a solution of the additive and ingested seawater, compares favorably with increasing the amount of fuel or capacity of the propulsion engine. On a poundfor-pound basis, the approach of internally mixing the polymer-drag reduction solution offers a greater potential in increasing torpedo range, or alternatively increasing torpedo speed, than does the addition of incremental amounts of fuel or engine capacity. This theoretical potential has prompted various attempts to devise a practical apparatus to implement this approach.

In some of these cases, the resultant apparatuses have not been able to introduce the polymer agent into solution at a sufficient concentration and with a sufi'icient solution flow rate to be eifective in reduction of drag. The serious difl'iculty which has confronted workers in these cases is the limitation imposed by the relatively low solution rates of the state-of-the-art forms of the polymer additive.

In another series of attempts, the polymer was added to ingested seawater by a continuous mixing device contained within the torpedo. While these efforts have been successful to a point, they have not resulted in practical use. One of the principle reasons behind this is the problem of packaging the mixer and dispenser necessary for such system. Present day torpedoes are principally intended for delivery from ship to target site by rocket propulsion, or for delivery by aerial drop. This has resulted in compactness becoming of primary concern, with severe restriction of the weight and size of the torpedo and all its components. With these criteria, the space penalty imposed by systems of mixers and dispensers has been considered to outweigh their advantages.

A further aggravation is that incomplete hydration of the polymer in the solution negates the effectiveness of the solution in providing drag reduction. In some instances this has resulted in a need for residence-time chambers in connection with the mixing apparatus.

An object of this invention is to provide an improved drag reducing apparatus, which may be conveniently packaged to make use of non-critical space in the nose fairing of a torpedo.

Another object is to provide apparatus in accordance with preceding objective which may be fabricated by inexpensive molding or casting processes.

A further object is to provide an improved torpedo apparatus for dissolving drag reducing polymer into ingested seawater at concentrations and solution flow rates which are effective for drag reduction purposes.

A still further objective is to provide an improved torpedo apparatus in accordance with the'preceding objective which causes hydration of the polymer material without need for auxiliary residence-time chambers. I

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a top elevation of a torpedo;

FIG. 2 is an enlarged central section of the nose of the torpedo, taken along lines 22, FIGS. 1 and 3, certain parts being shown in side elevation;

FIG. 3 is a partial section taken along lines 33 of FIG. 2; and

FIG. 4 illustrates modification of the invention.

Referring now to the drawing, and in particular to FIGS. 1 and 2, drag reducing apparatus in accordance with the present invention is illustrated in connection with a blunt nosed antisubmarine warfare acoustic torpedo 10. Torpedo 10 is conventionally formed as a plurality of disconnectable axial sections including a nose section 10a and a main body section 10b. Nose sections 10a has the type of hydrodynamic shape consisting of a flat nose face 12 and a zone of gradual fairing for approximately 0.8 of the length of the nose section. The fairing depicted in the drawing is conventional and is known as the cavitation bubble profile shape.

The intended purpose of the torpedo is the attacking of submerged submarines at their operating depth, and therefore requires a hull structure capable of withstanding the high hydrostatic pressures at such depths. In nose section 10a this requirement is met by an inner pressure hull 14. The hydrodynamic surface is formed by an outer fairing wall 16. (In main body section 10b there is only one hull, which serves as both the pressure and hydrodynamic hull.) Pressure hull 14 is only slightly larger in diameter than the nose face 12, and is provided with an outwardly projecting annular flange portion 14a at its rear end. The fairing wall 16 is fastened in place by means of a plurality of screws 18 (only one shown) which fasten its rear marginal edge to flange portion 14a. The construction is such that outer surface of the fairing merges with that of main body section 10b. Ahead of wall 16, the fairing is formed by a small ring 20 threaded upon the outer surface of pressure hull 14. The front edge of the fairing wall 16 is spaced slightly rearward from ring 20 forming a circumferential siot 22 which extends continuously about the torpedo nose. Conventional components otherwise shown in the drawing include acoustic transducer apparatus 24 with its protective face cap 26 of rubbery material. A suitable torpedo joint 28, in part formed by flange portion 144:, secures nose section a to main body section 19b.

The space between fairing wall 16 and pressure hull 14 forms an annular chamber 39. Four equiangularly spaced, laterally projecting, scOOps 32 open into the rear end of chamber 30. Scoops 32 serve to ingest seawater into chamber 30 under forward motion of the torpedo, forming the input of a Water circulation circuit through the chamber. The previously described slot 22 between fairing wall 16 and fairing ring 20 forms the outlet of this circuit. If desired, pop-up scoops, such as conventionally used as intakes for torpedo seawater batteries, may be substituted for the fixed projecting scoops. Such popup scoops are initially retracted within the hull line, and are actuated to their laterally projected position after the torpedo enters the water, as for example, in response to a seawater switch.

The present drag reducing apparatus employs the well known principle of ejecting a water solution of polymer drag reducing agents into the boundary layer flow about the torpedo. The drag reducing agent is provided by an ablative cake 34, FIGS. 2 and 3, of plasticized polymer disposed in chamber 39. The cake of plasticized polymer is annular in shape and is adapted to be radially foraminous by a provision of closely spaced radially holes 36 throughout its entire structure. The holes 36 are preferably formed by a molding or casting process. Three annular rings 33a, 38b and 380 are integrally molded into the outer surface of the annular cake. These rings are uniformly axially spaced with their outer portions projecting radially outwardly from the surface of the cake. A pair of similar rings 43a and 4% are integrally molded into the inner surface of the annular cake with their inner portions radially inwardly projecting from the inner surface of the cake. The projecting portions of rings 38 and rings at are sized to support the foraminous cake in a radially centered position within chamber 30, and a pair of locking rings 42a and 421; secure the cake against axial motion. Suitable metal inserts 44a and 44b are integrally molded with the cake at its rear and front end to provide a non-erosive abutting surface for engagement with the locking rings. In addition to their function of radially supporting the cake, rings 38 form a set of uniformly spaced baffles which obstruct the annular space between the outer surface of the cake and the fairing wall 16. Similarly locking rings 42a, ring 40a, ring 40b, and locking ring 4212 form a uniformly spaced set of baffles which obstruct the annular space between the inner surface of the cake and pressure hull 14. These two sets of bafllcs are axialy disposed in a staggered arrangement by which individual bafiies of one and the other of the sets are disposed in alternate axial succession. It will be apparent that what is provided is a series of labyrinth baffles which directs the seawater to flow alternately radially inwardly, and radially outwardly, through successive axial sections 34a, 34b, etc. of the radially foraminous cake. These axial sections 34a, 3417, etc. are defined between successive bafiie elements of the staggered series.

The drag reducing agent polymers which may be used in compositing the cake material are characteristically water soluble. In compositing the ablative plasticized polymer material, all ingredients should also be chosen to yield a composition which is readily soluble in water. An example of a suitable composition is disclosed in the copending applcation of Alexander B. Arranaga entitled Water-Soluble Poly(ethylene oxide) Plastic Composition. Briefly, that composition comprises a finely powdered high molecular weight form of poly(ethylene oxide) plasticized by means of a low molecular weight form of liquid polypropylene glycol, with a filler consisting of finely powdered polyvinylpyrrolidone. Polypropylene glycol is a thermoplastic type of plasticizer. Other minor amounts of wetting agent and stabilizers are also present.

The operation of the present drag reducing apparatus will be readily apparent from the preceding description. Water taken in under ram pressure through scoops 32, is circulated through the bafile labyrinth, which directs it through successive axial sections of the radially farominous cake of polymer material. This water circulation circuit places the flow in contact with a large effective surface area of the cake. The seawater flow ablates the lateral surfaces of the radial holes 36, and the ablated particles of the cake material go into solution in the flow. The solution is then ejected from slot 22 and swept back into the boundary layer by the ambient stream.

In the case of the given exemplary composition of the ablative cake 34 of the plasticized poly(ethylene oxide), it has been found that the plasticized polymer becomes partially hydrated before it is ablated by flow. As a result the polymer is hydrated to the desired degree as it fiows from slot 22. However, in instances in which plasticized polymer material may not hydrate this rapidly, the invention may be modified by provision of a battle labyrinth, constructed of simple metal plate stock, at the front end of the chamber. Such a labyrinth would be designed to provide the residence time needed to achieve the desired degree of hydration of ejected solution.

FIG. 4 shows a modification of invention which employs an annular slot 46 opening into the frontal face of the torpedo as its input. This location of the input in combination with location of exit slot 22 in a zone of negative dynamic pressure in the fairing, takes advantage of the large differential pressure between these two 10- cations in forcing the water through the water circuit. The polymer cake 34 therein is adapted to be radially foraminous by provision of radial holes (not shown), just as in the case of the FIG. 1.

While radial holes 36 are shown as uniform sized holes, an alternative would be to taper these holes to allow for a uniform erosion pattern. Another alternative would be to increase their size in the direction from the water influx end to the water efiiux end of the ablative cake. With these geometric variations, the desired flow or velocity uniformity could be obtained.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a torpedo, apparatus for producing an aqueouspolymer hydrodynamic drag reducing solution using ingested seawater as the solvent, said apparatus comprising;

(a) said torpedo being of the type having a generally cylindrical hydrodynamic hull,

(b) a longitudinally extending annular chamber formed underneath said hull, said channel having a solvent inlet end for receiving the ingested seawater solvent, and an outlet end forming a collection zone for the output of the apparatus,

(c) an annular, radially foraminous, cake of an ablative and water soluble drag reducing type of polymer material, and means for supporting same in a radially centered disposition in said annular channel, thereby forming an inner annular space between the inner surface of the annular cake and the inner wall of the annular chamber and an outer annular space between the outer surface of the annular cake and the outer wall of the annular chamber, and

(d) a means in part disposed in said inner annular space and in part disposed in said outer annular space, said means being for directing the flow of ingested seawater alternately radially inwardly, and

posited with a water soluble thermoplastic plasticizer and a water soluble filler.

References Cited UNITED STATES PATENTS 3,196,823 7/1965 Thurston 1l4--20 X 3,230,919 1/1966 Crawford 1l4--67 3,290,883 12/1966 Giles et a1 ll467 X BENJAMIN A. BORCHELT, Primary Examiner. G. H. GLANZMAN, Assistant Examiner. 

